It depends on the intensity of the tornadoes and the construction of the house. Damage can range from minor damage to the outside to complete destruction. Most tornadoes are weak, rated EF0 and EF1.
An EF0 may strip off small sections of roof surface and siding and take down gutters and awnings.
An EF1 may severely strip the roof, break windows, and sometimes break down exterior doors. Houses with weak roof attachments may lose their roofs.
And EF2 will most like remove all or large sections of the roof and some exterior walls may collapse. Some houses may shift off their foundations.
An EF3 will likely destroy exterior and interior walls. Weaker houses may collapse completely.
An EF4 will likely cause complete collapse of the house, though in strong houses a few interior walls may remain standing. Weakly anchored houses may be lifted up and carried some distance.
An EF5 will most likely blow a house clean off its foundation.
The tornado is a twister before it hits the ground, it just spins in the sky, kind of
Nothing happens. The lightning will not affect the tornado.
Damage is done to varying degrees depending on the intensity of the tornado on the Fujita scale.
it stays on the ground until it weakens
The tornado is not affected. It will continue though the valley as it would over any other terrain.
There is a good chance that your house will be damaged by high winds and debris.
Air at ground level will then spiral into the tornado and reach great speeds. Any buildings or trees the tornado hits will be damaged or destroyed by the winds.
House Tornado was created in 1988.
Trees and vegetation in the path of the tornado may be damage or destroyed. Exceptionally violent tornadoes may scour away grass and even soil.
No house can offer 100% protection from a tornado. The best option is a house with a basement to go to in case of a tornado.
If your house is hit by the full force of an F4 (now EF4) tornado it will probably be completely leveled. Even if you escape the worst of it (which can be surprisingly likely depending on the tornado) there will still likely be severe damage. The best place to be in an event like this, or any tornado, is in a storm cellar or basement.
If a tornado hits a body of water (at which point it is called a waterspout) it can "suck up" some unlucky fish. These fall back to earth a little later.